There is, of course, no way to answer this objectively. What would have happened if Hitler had died in WWI? Would WWII still have happened? The Holocaust? There is no way to prove this one way or the other.
My own argument is that Hitler was not "event-making" with regard to WWII. Many Germans surely felt angry about WWI and would have taken the same actions Hitler did. Those actions were not especially radical. It is likely that other Germans had the leadership skills and charisma to help Germany move towards acceptance of this war.
I would argue that Hitler was "event-making" with regard to the Holocaust. Yes, there was widespread anti-Semitism, but few people would have felt it as strongly as Hitler. Few people would have been as motivated as he was to destroy the Jews.
But again, this is all just conjecture. We can never know this for sure.